1. Field of the Invention
The present invention relates to a matrix switch of an optical waveguide type and a method for manufacturing the same and, more specifically, to a matrix switch of an optical waveguide type constituting a matrix switch comprising a uniform groove having a deep vertical cross section and with low transmission loss variations, and a method for manufacturing the same.
2. Description of the Related Art
In recent years, by virtue of the development of optical communications network, there is a large variety of digital information transmitted via optical fibers so that it is envisaged to diversify the pertinent services and upgrade the relevant networks. Under these circumstances, there is an increased need for optical switches and also for large-scale optical switches.
As a typical optical switch, a matrix switch of a bubble type is known. Given the number of inputs and outputs as m and n, respectively, in the bubble type matrix switch, m mutually parallel optical waveguides and n mutually parallel optical waveguides intersect and at each of the intersections a groove is formed, the core portion of mutually intersecting optical waveguides being cut. The grooves are filled with a matching oil having the same refractive index as that of the optical waveguide so that light can pass therethrough. Below the groove, a heater is provided so that bubbles can be created in the groove by heating. Since the refractive index is changed abruptly at the bubble and the matching oil interface plane, light will be totally reflected there. By adjusting the angle of the totally reflected light it is possible to make the light pass through a desired optical waveguide.
Conventionally, for a matrix switch, quartz glass is used that can realize a waveguide with low transmission loss. Quartz glass (SiO2) is dry-etched with a CHF-based gas. However, since the bond energy of Si—O is large, a large amount of energy is necessary for active species to break the bond, and main species contributing to the etching are ions capable of being accelerated through electrical voltage. In dry-etching to which ions mainly contribute, there has been a problem that, since a direction of acceleration voltage affects significantly the shape of etching, in a narrow groove with high aspect ratio, the sidewall acts as shadow to reduce the number of ions reaching the bottom, resulting in decrease of the etching velocity.
Further, due to the sidewall's shadowing effect, the bottom of the groove is not uniformly irradiated with ions and the cross section contour tends to be tapered. Furthermore, there has been a problem that when the proportion of the parts to be etched exceeds that of the parts being masked, the amount of ions reaching the bottom of the groove differentiates, causing the etching to tend to be non-uniform. Therefore, conditions for etching must be necessarily controlled accurately, resulting in decreased throughputs, as well as device functionalities and increased device costs.
The object of the present invention is to provide a matrix switch of an optical waveguide type with low transmission loss variations comprising uniform grooves with a deep vertical cross section and a method for manufacturing a matrix switch of an optical waveguide type for forming uniform grooves economically.